Among terminal devices, such as notebook PC, mobile PC and PDA, which comprise a first casing provided with a keyboard portion and a second casing provided with a display portion, uniaxial hinges are sometimes used, wherein the hinges connect the first casing and the second casing, such that both casings can open and close in an upward and downward direction; in other cases biaxial hinges are employed, wherein each of the hinges comprises two axes, wherein the second casing can further rotate with regard to the first casing in a horizontal direction, after the former opens 90 to 180 degrees relative to the latter. The present invention relates to the biaxial hinge of these categories.
Conventionally, a biaxial hinge of the above-mentioned structure is known, such as the one disclosed in JP Laid-Open Patent Application No. 2009-063039. The biaxial hinge according to the patent document is characterized in that a shaft attached to a first member (first casing) is connected to a further shaft attached to a second member (second casing) via a joint arm, and that a mechanism for generating friction torque is provided on each shaft, and that a link arm is provided; however, the hinge is not so designed that the first member can open more than 180 degrees relative to the second member.
Therefore, a parent company of this Applicant has proposed a biaxial hinge which can meet the above-mentioned requirements (JP Patent Application No. 2013-247542). The configuration of the biaxial hinge is characterized in that a first hinge shaft attached to the first casing side is coupled in parallel to a second hinge shaft attached to the second casing side, via a first joint member and a second joint member; that the first hinge shaft and the second hinge shaft are provided such that the former can rotate relative to the latter; and that a first mechanism for selectively restricting rotation and a second mechanism for selectively restricting rotation are provided between the first hinge shaft and the second hinge shaft, wherein the first mechanism selectively allow the first hinge shaft to rotate and the second mechanism have similar functions on the second hinge shaft; the first and the second mechanism for selectively restricting rotation are constructed such that both mechanism allow the first and the second casings to open and close in a prescribed sequence between the closed state at 0 degree and the opened state at 360 degrees.
In the above-mentioned prior art, a first mechanism for selectively restricting rotation comprises a locking member provided between a second joint member and a slide guide member, such that the locking member can slide in an upward and downward direction between a first hinge shaft and a second hinge shaft, wherein the locking member comprises a first cam convex portion in an upper portion and a second cam convex portion in a lower portion; a first mechanism for selectively restricting rotation further comprises a first A locking cam member having a first A cam concave portion and a first B cam concave portion, wherein the first A locking cam member is provided above said locking member, and wherein the first hinge shaft passes through and engages with the first locking cam member, and a first B locking cam member having a second A cam concave portion and a second B cam concave portion, wherein the first B locking cam member is provided below the locking member, wherein the second hinge shaft passes through and engages with the first B locking cam member. On the other hand, a second mechanism for selectively restricting rotation comprises a second A locking cam member attached to the first hinge shaft, wherein a rotation of the second A locking cam member is restrained by the first hinge shaft; a second B locking cam member attached to the second hinge shaft, wherein a rotation of the second B locking cam member is restrained by the second hinge shaft; a movement stopper rotatably provided between the second A locking cam member and the second B locking cam member, wherein the movement stopper engages with the second A locking cam member and the second B locking cam member, under specific conditions depending on a rotation angle of the movement stopper; a first stopper lever rotatably attached to the first hinge shaft to engage with the movement stopper, wherein the first stopper lever is brought into a pressurized contact with the second A locking cam member; and a second stopper lever rotatably attached to the second hinge shaft to engage with the movement stopper, wherein the second stopper lever is brought into a pressurized contact with the second B locking cam member.
However, a further problem arises, in that there are too many components involved and the structure is too complex, which leads to a high manufacturing cost. A manufacturer of terminal devices such as notebook PC would set very strict demands for reducing the costs of the components of the terminal devices.